Alternating current voltage regulator



Feb. 4, 1941. HANSELL 2,230,945

ALTERNATING CURRENT VOLTAGE REGULATOR Filed Nov. 4, 1958 4 Sheets-Sheet 1 Inventor-z John B. 'Hansell,

by WW I His Attorney.

Feb. 4, 1941. J, a. HANSELL ALTERNA'IING CURRENT VOLTAGE REGULATOR Filed Nov. 4, 1958 4 Sheets-Sheet 2 Fig.6.

Inventor: John B. Hansell,

His Attorn e Feb. 4, 1941. v HANSELL 2,230,945

ALTERNATING- CURRENT VOLTAGE REGULATOR Inventor: John B. Hansel I,

H is Atto'rn 22 Patented Feb. 4, 1941 UNITED STATES ALTEBNATING oUnaENT VOLTAGE nncnm'roa John Bentley Hansell, Pendleton, England, assignor to General Electric Company, a corporation 0! New York Application November 4, 1938, Serial No. 238,925 In Great Britain November 17, 1937 4 Claims.

This invention relates to alternating current voltage regulators.

According to the present invention an alternating current voltage regulator is'provided comprising in combination a primary winding including a plurality of coils connected, or adapted to be connected in series across a primary or supply circuit, a magnetic circuit structure providing independent magnetic circuits for said windings and having one or more relatively movable members of magnetic material forming part of said magnetic circuits for each primary winding and adapted to vary the relative reluctances of each of said magnetic circuits, and a secondary winding including one or more coils closely electromagnetically coupled by said magnetic circuit structure with a coil or with respective coils of said primary winding, whereby the relative voltage distribution across said primary coils may be adjusted by relative movement between the parts of said structure, thereby to adjust the voltage or voltages induced in the secondary coil or coils by the associated coil or coils of the primary winding.

As will be understood, the magnetic circuit structure, including the relatively movable member or members thereof, may assume various forms so that the reluctance of the magnetic circuits of the several primary coils are adjustable by relative movement between said structure and said member or members, thereby to adjust the relative voltage distribution between said coils and the relative voltage or voltages induced in the secondary coil .or coils, and such relative movement may be effected in any convenient manner, either by manual operation or otherwise.

In a preferred construction of the regulator, according to a further feature of the invention, said regulator comprises a plurality of cores provided with poles projectin? towards a central space between said cores,- in which space is located one or more core members of magnetic material adapted variably to bridge the gaps between such poles, and the coils of the primary and secondary windings are disposed in the slots between said poles and surround the path of movement of said core member or members, together with means for effecting relative movement between said core member or members and said poles along said central space so as to change the reluctances oi the magnetic circuits of said primary coils with respect to one another, and thereby to adjust the distribution of voltage between'said primary coils. Prefverably two cores are provided with adjacent poles thereof disposed opposite and parallel with one another.

Generally the magnetic circuit structure in which the coils are arranged will be fixed whilst by means of bolts I5.

the one or more co-operating cores or members will be movable, although the invention is not limited to such arrangement for obtaining the relative movement between said structure and said core or cores.

In order that the invention may be more fully understood reference will now be made by way of example to the accompanying drawings, in which:

Figure 1 is a sectional side elevation of a preferred construction of the regulator according to the invention.

Fig. 2 is a part sectional plan taken on the line IIII of Fig. 1.

Figs. 3 to 10 inclusive illustrate diagrammatically a number of examples of winding arrangements of the regulator.

Referring first to the preferred embodiment of the invention shown in Figs. 1 and 2, the regulator comprises two fixed laminated cores 1 and 2 which are clamped between side plates 3 and 4 with interposed packing pieces 5 by means of clamping bolts 8. The plates 3 are supported from a cover plate I of a cylindrical casing 8 for the regulator, the plates 3 being provided with flanges 9 which are bolted as indicated at ID to said cover plate. The laminae oilthe cores i and 2 may be located in place by cross bars ll welded to said laminae and screwed to said flanges 9.

The cores l and '2 are each provided with a plurality of poles 12, three such poles being provided in the example shown thereby to form slots or recesses such as A and B in which the coils 100 of the windings oi the regulator are disposed, the end plates 4 being provided with openings 4a adjacent the slots A and B for accommodating said windings. A movable core II of laminated construction is disposed in the central space between the-poles ii of the two cores, the laminae of the moving core bein clamped together between end clamping bars H The edges of the bars register with the inner vertical faces at I6 of the packing pieces 5 whereby the core [3 is slidably located between the cores I and 2.

A threaded rod H is fixedly secured to the upper end of the core 13 so as to carry the latter. This rod is threaded through an operating nut l8 having an extension I8 projecting through a central perforation in the cover plate I and secured againstaxial movement therein by means of a thrust collar 20. The nut 18 is counter-bored at its upper end and receives a boss 2| formed integrally with an operating hand lever 22, the rod i'l extending through the boss 2! and having screwthreaded engagement therewith as well as with the nut 18. The operating lever 22 is thus capableoi rotational movement with respect to the nut i8 but is locked in place with respect to said nut by means of a set-screw 23. By this means the screw-thread clearance between the nut I8 and the rod I I may be taken up so as to prevent chattering of the rod I'I against said nut.

The coils I surround the moving core I3 as shown in Fig. 2. The coils of the windings may be connected in various ways as hereinafter indicated but whatever connection is employed it will be seen that with the moving core I3 in its illustrated central position the reluctances of the magnetic circuits for the coils in the slots A will be similar to that of the magnetic circuits for the coils in the slots B. By rotation of the hand lever 22, however, the core I3 may be moved axially with respect to the fixed cores I and 2 in either direction. If, for example, the core is raised the reluctance of the magnetic circuit for the coils in the slots A will be reduced, whilst the reluctance of the magnetic circuits for the coils in the slots B will be increased and since the coils comprise coils connected in series with one another across a primary circuit the voltage distribution between said coils will be correspondingly varied, namely when the core I3 is raised from its central position a larger proportion of the primary applied voltage will appear across the primary coil in the slot A than across the primary coil in the slot B, and the voltage or voltages induced in any secondary coil or coils provided in the slot A or in the slot B will be correspondingly affected. On the other hand, if the core I3 is lowered with respect to the cores I and 2 then the reluctance of the magnetic circuit for the coils in the slots B becomes less than that of the magnetic circuit of the coils in the slot A so that a greater proportion of the primary applied voltage will now appear across the coils in the slots B than those in the slots A with a consequent change in the voltage or .voltages induced in any secondary coil or coils provided in the slot A or slot B.

When the core I3 is raised to' its uppermost position as indicated by the chain lines at I3a, the reluctance of the magnetic circuit for the coils in the slot A will be reduced to a minimum whilst that of the magnetic circuit for the coils in the slots B will be increased to a maximum and consequently nearly the whole of the primary applied voltage will appear across the coils in the slots A. Similarly, when the core I3 occupies its lowermost position substantially the whole of the primary applied voltage will appear across the coils in the slots B. It will thus be seen that by operation of the lever 22 the voltage distribution between the coils may be progressively adjusted from the condition in which maximum voltage appears across the primary coil in slots A and maximum voltage is induced in any secondary coil or coils in said slots A to that in which the maximum voltage appears across the primary coil in the slots B and maximum voltage is induced in any secondary coil or coils in said slots B.

The rod I1 may be provided at its upper end with a stop collar 25 for limiting the downward movement of the rod I1 and core I3, and the rod may be calibrated in any suitable manner, for example, by having a slot 26 machined therein in which slot is received a scale 21 which may have suitable indications thereon for showing the position of the core I3.

The cover plate I may conveniently carry terminal boxes 28 for the connection of the windings in circuit.

Preferably, the moving core I3 is formed of a reduced width over a middle portion of its length, namely at 29 for a purpose which will hereinafter be explained with reference to Figs. and 6.

As will be appreciated, the coils in the fixed cores I and 2 may be arranged and connected in various ways according to requirements. In the example illustrated diagrammatically in Fig. 3 in which the fixed cores are each provided with three poles, there is employed a primary winding comprising two coils IN and I02 connected in series with one another across primary circuit conductors I03 and I04 the coil IOI being wound in the slots A'between the upper and centre limbs and the coil I02 being wound in the slots B be-- tween the centre and lower limbs of the two cores. A secondary winding is provided comprising two coils I05 and I06, the coil I 05 being disposed in the slots A with primary coil I M and the coil I06 being disposed in the same slots B with the primary coil I02. The secondary coils I 05 and I06 are thus closely coupled electromagnetically with the primary coils IOI and I 02 respectively. The coils I 05 and I05 are connected in series with one another and with output leads I01 and I03.

In operation, with the sliding core I3 in its uppermost position, the reluctance oi the magnetic circuit for the coil I M will be minimum, the flux paths for said coil being as indicated by the broken lines in Fig. 3. On the other hand, the reluctance of the magnetic circuit for the coil I02 will be a maximum since the lower end of the sliding core I3 has been withdrawn completely from said coil. Under these conditions, the voltage across the conductors I03 and I04 appears mainly across the coil IOI and only a small proportion of the applied voltage appears across the coil I02, since the reluctances of the magnetic circuits of the coils IOI and I02 are respectively small and large. As a result, substantially no voltage is induced in the secondary coil I02 whilst maximum voltage is induced in the secondary coil IM and the output leads I01 and I00 and apparatus connected therewith will be energised accordingly. It now the core I3 is lowered, the reluctance of the magnetic circuit for the coil IOI will be progressively increased and the reluctance of the magnetic circuit for the coil I02 will be progressively reduced, with the result that the proportions of the primary applied voltage appearing across the coils IOI and I02 are respectively progressively reduced and increased. Consequently the voltages induced in the secondary coils I05 and I03 are progressively reduced and increased respectively until when the core I3 occupies its lowermost position as indicated by the chain lines in Fig. 3 maximum voltage is induced in the coil I 00 and only small voltage in the coil I 05, the reluctance of the magnetic circuits for the coil I02 being then a minimum whilst the reluctancesot the magnetic circuits for the coil IOI are a minimum, so that the primary voltage appears mainly across the primary coil I02 and only a small proportion of said voltage appears at the primary coil III. Consequently, substantially no voltage is induced in the secondary coil I05 and maximum voltage is induced in the secondary coil I00.

Since the secondary coils I05 and I05 are connected in the secondary circuit (leads I I1 and 400) reversely with respect to one another, whilst the primary coils III and I 02 are connected in the same direction as one another in the primary circuit, the voltage imparted to the conductors I01 and I08 by the coil I05 will be reversed with respect to the voltage imparted to said conductors by the coil I05. Thus, with the core I3 in its lowermost position the leads I01 and I 03 and output circuits will again be energised at maximum voltage but in phase opposition to the conditions when the core I3 occupies its uppermost position.

In a central position of the core I3 the primary applied voltage will be equally divided between the two coils IN and I02 and equal voltages will be induced in the two secondary coils I05 and I06 so that no resultant voltage is imparted to the leads I01 and I08. By movement of the core I3 from its uppermost to its lowermost position the voltage across the leads I01 and I may thus be progressively reduced from a maximum value to zero and then increased to a maximum value in counter-phase.

As will be appreciated, the ratios of the numbers of turns of the respective pairs of primary and secondary voltages may be chosen to give any required output voltage, whilst the ratio of the numbers of turns of the primary coils may be chosen so as to give the desired variation in the voltage distribution between said coils.

Fig. 4 illustrates a modification of the arrangement of Fig, 3 in which only one secondary coil, I05, is employed, connected directly across the secondary output leads I01 and I09, such ar rangement being useful where it is required to obtain at the leads I01 and I09 a voltage progressively adjustable between zero and a. maximum value but where it is not required to reverse the phase of the secondary voltage.

Fig. 5 illustrates a modification of the connections of the secondary coils of an arrangement as" in Fig. 4, whereby an adjustable boost and buck of the primary voltage may be obtained. Thus with the arrangement of Fig. 5, the load 40 apparatus (not shown) to be supplied from the 5 the two secondary coils I05 and I06 in series with one another, said coils, I05 and I06 being however connected in opposition with one another between the lead I09 and conductor I08.

Assuming the coils IM and I05 to be wound in 50 the same direction as one another and the coils I01 and I06 to be wound in the opposite direc-' tion to one another, the two primary coils being wound in the same direction as one another, then the coil I05 will produce between the'leads I03a and I09 a voltage opposing the voltage across the conductors I03 and I04 and the coil I06 will produce between said leads a voltage assisting the voltage across said conductors. With the core I3 in the uppermost position the coil I05 produces maximum voltage and the-coil I06 produces substantially no voltage so that a reduced voltage is obtained across the leads mm and I09. The voltage across the leads NM and I09 may be progressively increased by downward movement of the core I3 whereby the voltage induced in the coil I05 is reduced and that induced in the coil I06 is increased, until when the core I3 reaches its central position the voltages induced in the coils I05 and I06 counterbalance one another and the leads MM and I09 are energised at the voltage of the conductors I03 and I04.

Continued downward movement of the core 53 results'in the voltage induced in the coil I06 becoming greater than that in the coil I05 so that the voltage applied to the leads "3a and I 09 is correspondingly greater than that at which the conductors I03 and I01 are energised. The

voltage of the said leads is progressively increased until finally when the core I3 occupies its lowermost position the maximum voltage is obtained.

In cases where it is desired only to obtain boosting of the yoltage the coils I05 may be omitted whilst in cores where it is required only to reduce the voltage of the leads I030 and I09 with respect to the input voltage the coil I06 may be omitted.

It has been stated above that the primary coils IM and I02 are assumed to be wound in the same direction, such arrangement having been found more convenient. It is however possible and within the scope of the invention to arrange said primary coils wound in opposite directions to one another, in which case, as will be appreciated, where there are two secondary coils which are required to produce voltages in opposition to one another, for example as in Figs. 3 and 4, such secondary coils will be wound in the same direction as one another so that said secondary coils are wound in opposite direction with respect to the direction of winding of their respective primary coils. With the primary coils wound in the opposite direction to one another the middle poles of the cores I and 2 carry the sum of the fluxes due to said two coils whereas with the latter wound in the same direction said poles carry only the difference of said fluxes.

The purpose of the recesses 28 in the sides of the core I3 as shown in connection with Fig. 1 may now be explained. Considering, for example, the arrangement of Fig. 5, with the core I3 in the illustrated position, and with the leads M301. and I09 open-circuited, the flux paths will be as indicated by the broken lines in Fig. 5, the flux a being due to the coil IOI. Similarly, when the core I3 occupies its central position, and again with the leads I03a and I09 openecircuited the flux paths will be as indicated by the broken lines a in Fig. 6, which shows the arrangement of Fig. 5 with the core I3 in the central position. When, however, the leads I03a. and I09 are loaded and current flows through the secondary coils I05 and I06, flux will be induced in the middle poles of the cores I and 2 as indicated by the broken lines I) and with a small air gap between the middle poles and the core H, the reactance of the coils I05 and I06 to load current may be undesirably high. In order to reduce this reactance, the core I3 is provided with the recesses 29 (Fig. 1) which are located adjacent the middle poles in the mid-position of the core I3. whilst still retaining desirably small air gaps between the core I3 and the operative poles of the fixed cores I and 2 when the core I3 occupies either extreme position.

As will be appreciated, although in Figs. 1 to 6 the fixed cores I and 2 are shown as having three 6 poles each, with the windings disposed in the two slots formed by said poles, it is within the scope of the invention to arrange said cores with any greater number of poles and slots as may be desired.

By way of example an arrangement employing four slots A, B, C and D in said cores is shown diagrammatically in Fig. 8, the arrangement of windings corresponding, also by way of example, with that of Fig. 5. In the arrangement of Fig. 7, the primary coil IIII is subdivided into two sections IM and IOI" disposed respectively in the two upper slots A and B of the cores I and 2, and the primary coil I03 is subdivided into two sections Hi2 and I02" disposed respectively in the two lower slots C and D of the cores I and 2. Similarly, the secondary coil I05 is subdivided into two sections I05 and H15" and the secondary coil Idli is subdivided into two sections I06 and Hi6", the sections I05, I05", I06 and I06" being disposed in the same slots as the primary coil sections IIlI', Illl, IOZand I02" respectively, so as to be closely electromagnetically coupled respectively with the latter. The moving core is of sumcient length so as in its extreme position to bridge between the uppermost pole and the centre pole on the one hand, and the centre pole and the lowermost pole on the other hand. Thus, in the uppermost position of the core I3 substantially the whole of the primary applied voltage appears across the coil sections Ill I and I I whilst in the lowermost position of the core I3 substantially the whole of said voltage appears across the coil sections I82 and I 02". In the centre position of the core I3 substantially the whole of the primary applied voltage appears across the coil sections IQI" and I02, being equally distributed therebetween. As will be appreciated, the tour secondary coil sections may be connected in any other desired manner, for example to correspond with Fig. 8, or only one set of coil sections, such as I and I05", or I08 and I96" may be provided, where only one secondary coil is required such as in Fig. 4.

In applying regulators according to the invention in polyphase systems a group of regulators each as hereinbefore described may be employed, one regulator for each phase, with means for simultaneously adjusting the movable cores of the several regulators. For example, a threephase regulator may comprise three regulators, each as described with reference to Figs. 1 and 2, with the three spindles geared together for simultaneous movement from a common operating member. In another arrangement the fixed cores of a single regulator are provided with slots accommodating the windings of the several phases and a plurality of moving cores, one for each phase, forming a single moving system, are disposed in line with one another and spaced along the central space between the fixed cores. The arrangement may be such that certain of the poles on the fixed cores are common to two of the moving cores as in the three-phase embodiment now to be described with reference to Fig. 8. In this arrangement each of the fixed cores I and 2 is provided with seven poles and six slots A to F inclusive. In the two upper slots A and B are disposed primary coils IIIIA and IB2A oi the first phase, in the two centre slots C and D primary coils IUIB and WEB of the second phase and in the bottom two slots E and F two primary coils' IBIC and W2C of the third phase. These pairs of primary coils are shown as being connected in delta with the three phase conductors MIA, IIIB and II IC, although as will be appreciated the said coils may alternatively be connected in star or in any other polyphase manner as may be desired. The adjustment of the voltage distribution across the coils IOIA and 502A is obtained by a moving core IZIA co-operating with the three upper poles of the fixed cores I and 2 whilst the voltage distribution across the coils IUIB and I828 is controlled by a moving core I33 cooperating with the three centre poles of the cores I and 2 and the voltage distribution across the coils Ill IC and W2C is controlled by a moving core I38 co-operating with the bottom three poles of the cores I and 2. The three moving cores I3A, I33 and I30 are connected directly with one another as indicated at I I 2 so as all to be movable together as a single moving system. It will be seen that the third pole, designated H3, from the top of each core I and 2 is common to both the moving cores I3A and I313, co-operating with the core I3B in the illustrated upper position of the regulator and with the core 13A in the lowermost position of the regulator. Furthermore, the third pole, designated H4, from the bottom of each fixed core is common to both the sliding cores I313 and I30, co-operating with the core I30 in the uppermost position of the regulator and with the core I3B in the lowermost position of the regulator.

The regulator of Fig. 8 is shown as provided with two secondary coils for each phase, namely at 305A and IDEA; IUSB and I068, and I050 and I060, which coils are in each phase connected similarly to the secondary coils in the arrangement of Figs. 5 and are respectively connected with three-phase output leads II5A, II5B and IISC as shown, whereby the regulator provides a progressively adjustable buck and boost of the voltage of said output leads with respect to the voltage of the three-phase input conductors I I IA, I I IB and II IC. Obviously, however, the regulator of Fig. 8 may be employed with any other arrangement of secondary coils, for example cor responding with the other single phase arrangements hereinbefore indicated.

In any polyphase arrangement according to the invention employing either a group of associated separate regulators for the several phases or an arrangement of the kind above described with reference to Fig. 8, the windings may be connected in any desired polyphase manner, and also in some cases a tertiary delta winding may be provided for stabilising the neutral point of the regulator system when a star connection of the windings is employed. This tertiary winding, whether applied to a polyphase group or" separate regulators or to unitary polyphase regulators such as that shown in Fig. 8, should preferably be divided with a portion in each slot of the regulator, and forms a delta circuit which may be idle as regards external circuits but which stabilises the neutral point of the main windings.

In a modified arrangement of unitary regulator for use with a three-phase system the regulator is provided with two sets of windings which are connected with one another and with the input conductors in open delta formation. With this arrangement, since only two sets of windings are required, the size of the regulator may be reduced. One such embodiment of the invention .is shown in Fig. 9, in which secondary coils are again shown by way of example for providing a buck and boost of the voltage of the output leads with respect to the input conductors. In this arrangement, the cores I and 2 are each provided with four slots A, B, C and D and primary coils IOIAC and IIJZAC connected between the input conductors IIIA and IIIB of the threephase system are disposed in the two top slots whilst primary coils IOICB and IIIZCB connected between the input conductors IIIB and I I I0 of the three-phase system are disposed in the two bottom slots. Two moving cores I3A and I3B are provided, being connected directly together for simultaneous movement as indicated at H2. the core I3A controlling the distribution of voltage across the coils IOIAC and I02AC and the core I3B controlling the distribution of voltage across the coils IOIBC and IU2BC.

or the three-phase output leads IIA, use and I I5C, the last mentioned is connected directly with the junction point of the two pairs of ZID primary coils IOIAC and MAC on the one hand and IOIBC and IOZBC on the other hand, that is to say, said lead N50 is connected directly with the conductor IIIC. The lead 5A is connected through secondary coils I05AC and IOBAC, associated respectively with the primary coils IOIAC and IMAC, with the conductor I I IA, said secondary coils acting in opposition to one another. The lead II5B is connected through secondary coils M5130 and IOBBC, associated respectively with the primary coils IOIBC and 1230, with the conductor II IB, said coils IMBC and IIIBBC also acting in opposition to one another.

The operation of the regulator of Fig. 9 will be apparent from the vector diagram of Fig. 10, in which the voltage between the conductor 1 I I3 and IIIA is represented by the vector BA and the voltage between the conductors IIIB and HIC is represented by the vector BC. To the vector BA is added the vector AA representing the difference of the voltages induced in the secondary coils IOSAB and IOGAB and to the vector BC is added the vector CC representing the difference of the voltages induced in the secondary coils I05CB and HJSCB. The resultant voltage across the output leads IISB and USA is thus represented by BA and the voltage across the output leads H513 and N50 is represented by BC. These conditions correspond with the position of the regulator shown in Fig. 9 in which the primary voltage mainly appears across the primary coils lOlAB and IUICB and the output voltages are consequently greater than the input voltages as above set forth. When, however, the position of the cores HA and I3B is adjusted so that the voltages induced in the coils IIJBAB'and 105GB are greater than those induced in the coils IUSAB and IBBCB, for example when the cores 13A and I3B occupy their lowermost positions and the input voltages appear mainly across the primary coils IUZAB and 12GB, the vectors AA and CC" are reversed in sense as indicated at AA" and CC" and the resultant voltages across the conductors H513 and NBA on the one hand and the conductors IISB and II5C on the other hand are represented by BA" and BC, being then smaller than the input voltages.

It will also be understood that the various winding arrangements hereinbeforeindicated in the foregoing description, although illustrated diagrammatically as being employed in regulators with the same general arrangement of cores as in the embodiment shown in Figs. 1 and 2, may be employed with any other equivalent arrangement of magnetic circuit structure and relatively movable core or cores falling within the scope of the appended claims.

I claim:

1. An alternating current voltage regulator comprising in combination, a primary winding including a plurality of coils connected in series, a magnetic circuit structure providing independent magnetic circuits for said coils, said structure having relatively movable members" of magnetic material forming part of the magnetic circuits for each primary coil and being operative to vary the relative reluctances of each of said magnetic circuits whereby the relative voltage distribution across said primary coils may be adjusted by relative movement. across the parts of said structure, and two secondary coils which are relatively closely electromagnetically coupled by said magnetic structure to said primary coils respectively, said secondary coils being connected in such directions with respect to one another that the voltages induced in said secondary coils are in opposition to one another whereby the voltage imparted to a secondary circuit by the secondary coils may be adjusted and reversed in phase by relative movement between the parts of the magnetic circuit structure.

2. An alternating current voltage regulator comprising in combination, a primary winding including a plurality of coils connected in series, a magnetic circuit structure providing independent magnetic circuits for said coils, said structure having relatively movable members of magnetic material forming part of the magnetic circuits for each primary coil and being operative to vary the relative reluctances of each of said magnetic circuits whereby the relative voltage distribution across said primary coils may be adjusted by relative movement across the parts of said structure, and two secondary coils which are relatively closely electromagnetically coupled by said magnetic structure to said primary coils respectively, said secondary coils being in a secondary circuit which is connected across said primary coils whereby the voltage imparted to the secondary circuit by the secondary coils may be raised above and lowered below the voltage across said primary coils by relative movement between the parts of the magnetic circuit structure.

3. An alternating current voltage regulator comprising in combination, a primary winding including a plurality of coils connected in series, a magnetic circuit structure providing independent magnetic circuits for said coils, said structure comprising a plurality of cores provided with poles projecting towards a central space between said cores in which space is located a core member of magnetic material adapted variably to bridge the gaps between said poles, said member being provided with recesses disposed between -its ends, a secondary winding including a. coil closely electromagnetically coupled by said magnetic circuit structure with a coil of said primary winding, said primary and secondary coils being disposed in the slots between said poles and surrounding the path of movement of said core member, and means for effecting relative movement between said core member and said poles along said central space so as to change the reluctances of the magnetic circuits of said primary I coils with respect to one another and thereby to adjust the distribution of the voltage between said primary coils.

4. An alternating current voltage regulator for a three-phase circuit comprising, a pair of windings connected in series between two of the phase conductors of said circuit, a second pair of windings connected in series between the remaining phase conductor of said circuit and a point on the circuit of the first -mentioned pair of windings, means for simultaneously oppositely varying the reluctance of the magnetic circuits of the windings constituting each pair, and a third pair of windings closely electromagnetically coupled respectively with one of the windings of the first and second pair of windings, said third pair of windings being so connected that voltage variations therein vary symmetrically the voltage of a three-phase circuit.

JOHN BENTLEY HANSELL. 

